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Post by Gary Cook on Mar 5, 2015 23:17:58 GMT -5
In the case of the XPA-1L, the amplifier is "35 watts per channel of Class A" - which is based on the power its output stage dissipates in Class A, and is independent of the impedance of the speaker you have connected (thus the same "Class A rating" into 4 or 8 ohms). Cheers Gary |
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Post by garbulky on Mar 5, 2015 23:50:51 GMT -5
hey, no one answered my question. since the XPA-1L puts out (in A/B) 250 watts into 8 ohms and 500 watts into 4 ohms...then why when in class A when it puts out 35 watts into 8 ohms it only puts out 17.5 watts into 4 ohms and not 70 watts (into 4 ohms)? since it can put out twice the amount (in A/B) into 4 ohms as it does into 8 ohms...then why when in A does in only put out half the amount into 4 ohms as it does into 8 ohms? I don't mind lookin like a dummy here. I want to know why this is. It's 35 watts in 4 or 8 Ohms. From another thread: The quoted specs by Lonnie is 35 watts for both 4 and 8 ohms. How they do it is nobody's idea. But it is not jumping to 70 watts in 4 ohms if that was your question. There are at least two things that cause the switch to class AB. First is the standard 35 watts bias. The other is a thermal bias that switches it to class AB mode when the heat gets past a certain amount. There may be a third control too. Why? I have no idea... More discussion here: emotivalounge.proboards.com/post/503745/threadIt references an email that Lonnie sent that also stated 35 watts in 4 & 8 ohms. From Keith's post, they were talking about the bias which is 35 watts regardless of speaker impedance...but the 4 ohm actual output to the speaker is 17.5 watts. Srange I know... |
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Post by willcycle on Mar 6, 2015 6:57:46 GMT -5
This is not strange at all and if you do the math you will see why. If you think of it this way it may help understanding. Your amplifier voltage rails are fixed by the power supply design. Bias is adjusted by setting a fixed quantity of current through the power transistors. If your output stage is biased to dissipate 35 watts of power into 8 ohms, and keeping in mind the bias current through the output transistors is a FIXED value, when you reduce your load impedance to 4 ohms you would normally require double the current. Since your bias current doesn't change you half the power (P=I2R).
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KeithL
Administrator 
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Post by KeithL on Mar 6, 2015 11:45:47 GMT -5
It would probably be technically easier to understand if the rating said something like: The XPA-1L operates at xx amps of bias in Class A mode, which allows it to remain in Class A for up to 35 watts with an 8 ohm load, and up to 17.5 watts with a 4 ohm load. Unfortunately, this isn't the way amplifiers are normally rated, and so it would confuse more people than not.  This is not strange at all and if you do the math you will see why. If you think of it this way it may help understanding. Your amplifier voltage rails are fixed by the power supply design. Bias is adjusted by setting a fixed quantity of current through the power transistors. If your output stage is biased to dissipate 35 watts of power into 8 ohms, and keeping in mind the bias current through the output transistors is a FIXED value, when you reduce your load impedance to 4 ohms you would normally require double the current. Since your bias current doesn't change you half the power (P=I 2R). |
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Post by jdaddabbo on Mar 6, 2015 14:00:29 GMT -5
Hey Keith, I for one can't Thank You enough for taking the time to respond to all of this (all of us), and with such indepth knowledge. Over the years I've gotten bits and pieces of info on this topic from a countless # of internet sites & forums (not just about these two Emotiva amps, but in general), and your explainations have been by far the most indepth and easy to understand, and therefore extremely HELPFUL. Thank you!!!
Ps. And it is the most Musical and Affordable 17.5 Class A watts into 4 ohms (30 watts for the XPA-1) that has ever run through my Legacy Audio Focus Speakers, and something I serious urge everyone to try out for themselves. If the 17.5 Class A watts into 4 Ohms / 35 Class A watts into 8 Ohms (w/peaks to 500 watts!) will suffice for your particular Speakers, Room and Volume habits then the XPA-1L will certainly put a Smile on your face. If however you tend to Listen a bit Loud (guilty as charged), then the 30 Class A watts into 4 ohms / 60 Class A watts into 8 ohms (w/peaks to 1000 watts!) of the XPA-1 will no doubt do the trick (it certainly has for me... my XPA-1Ls now serve the DSX Wide channels, as does a 3rd XPA-1L power my Center channel, with 2 pairs of XPA-3s powering the Height, Side and Rear Surround channels).
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Post by DavidR on Apr 9, 2015 22:02:24 GMT -5
since the XPA-1L puts out (in class A/B) 250 watts into 8 ohms and 500 watts into 4 ohms...wouldn't it be the opposite of what jdaddabbo says, wouldn't the XPA-1L in class A mode put out 35 watts into 8 ohms and 70 watts into 4 ohms? Good point. Odd that the info provided on both of the monoblocks only states Class A watts into 8 ohms. |
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Post by swissie on Apr 10, 2015 7:12:09 GMT -5
I'm relieved to hear that 35 W of class A are available, regardless of load impedance. Looking at a impedance curve for my little XQ-20s, they are rated at 8 ohms, peak at 16 ohms and trough at 3.2 ohms (my sub-woofer handles everything below 100 Hz). As far as I am aware, very few louudpeakers have a linear impedance curve. Key here, must be for the amp to drive any load put in front of it, which the XPA-1L appears to do very well. I doubt I ever get above 35W, except for Demos of course. |
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Post by garbulky on Apr 10, 2015 16:52:50 GMT -5
I'm relieved to hear that 35 W of class A are available, regardless of load impedance. Looking at a impedance curve for my little XQ-20s, they are rated at 8 ohms, peak at 16 ohms and trough at 3.2 ohms (my sub-woofer handles everything below 100 Hz). As far as I am aware, very few louudpeakers have a linear impedance curve. Key here, must be for the amp to drive any load put in front of it, which the XPA-1L appears to do very well. I doubt I ever get above 35W, except for Demos of course. The XPA-1 L will output 17.5 watts of class A power to 4 ohm speakers. However it is biased at 35 watts of power at its bias point which translates to a real world 17.5 watts of class A that the 4 ohm speaker will see. I think you can say that a 2 ohm speaker will see half of 17.5 |
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Post by donmobliano on Jan 16, 2016 19:44:34 GMT -5
Old thread I know, but hopefully someone can also answer this. Given the above information, would it be correct to assume that the XPA-1L would output Class A up to 70 watts under a 16ohm load?
I'm looking to bi-amp (2) Paradigm Prestige 75F speakers with (4) XPA-1L's. I'm not sure what the impedance will be for the high and low ends of the speakers once they are separated, but the load is supposedly 8ohm when they're combined.
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Post by garbulky on Jan 17, 2016 2:17:52 GMT -5
Old thread I know, but hopefully someone can also answer this. Given the above information, would it be correct to assume that the XPA-1L would output Class A up to 70 watts under a 16ohm load? I'm looking to bi-amp (2) Paradigm Prestige 75F speakers with (4) XPA-1L's. I'm not sure what the impedance will be for the high and low ends of the speakers once they are separated, but the load is supposedly 8ohm when they're combined. DONT THINK IT works that way (70) |
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Post by donmobliano on Jan 18, 2016 3:16:00 GMT -5
Old thread I know, but hopefully someone can also answer this. Given the above information, would it be correct to assume that the XPA-1L would output Class A up to 70 watts under a 16ohm load? I'm looking to bi-amp (2) Paradigm Prestige 75F speakers with (4) XPA-1L's. I'm not sure what the impedance will be for the high and low ends of the speakers once they are separated, but the load is supposedly 8ohm when they're combined. DONT THINK IT works that way (70) Per this thread - emotivalounge.proboards.com/thread/45420/class-amplifier-performance-ohm-loads
It looks like it does transition at 70 watts, per boomzilla:
Thank you Mr. Cook - exactly correct. The remainder of this is simple volts x amps = watts. Change one, change the other two. The other significant equation is Ohm's law where E/IR applies. E is volts or Electro-motive force, I is amperes or current, and R is resistance (or in the case of a speaker, impedance which takes into account not only the speaker's resistance, but also its inductance and capacitance. So speaking, specifically, of the XPA-1L, as the resistance drops to half, the current doubles. Therefore, for an 8 ohm load, 35 watts of Class A before the transition occurs. For a 4 ohm load, 17.5 watts of Class A before the transition occurs. For a 2 ohm speaker, you'd get but 8.75 watts. If you had a 16 ohm speaker (old Electro-Voice, maybe) you'd get 70 watts of Class A before the transition. In a nutshell, this is one of the reasons why Class-A Single-Ended-Triode tube amps DON'T like low impedance loads. They have no "automatic transition to class AB." When their maximum wattage is exceeded, they clip - period. Clear as mud? Guess I'll just have to try it out. 
I'm also assuming that the XPA-1L will output 125 watts RMS at 16 ohms (half of 250 watts at 8 ohms).
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Post by garbulky on Jan 18, 2016 10:53:32 GMT -5
its not been confirmed by emotiva. at that logic 32 ohms gets 140 watts...
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Post by donmobliano on Jan 18, 2016 11:53:16 GMT -5
its not been confirmed by emotiva. at that logic 32 ohms gets 140 watts... True, however the RMS wattage would drop to 62.5 watts, so I guess at that point there wouldn't be a bias transition at all and you would be in class a all the time. |
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Post by jdaddabbo on Jan 18, 2016 13:04:56 GMT -5
Your Paradigm Prestige 75F speakers are only 8 ohm "compatible", and they often dip to 4 ohms and stay there... like through a good part of the lower mids. And then again in the upper frequencies. If I were you (because it is TRUE), I would consider the 75F's as 4 ohm speakers and nothing less. Bi-amping doesn't magically make them 8 ohm speakers, and surely not 16 ohm speakers.
Ps. And Yes, I am correct about the power rating. Sorry, sounds like you would be much better off with a Pair of XPA-1 Gen 2 than Bi-amping. As well I would much rather drive a pair of 95F's with only two XPA-1L Gen 2s, then to put my money into the 75F's and two pairs of XPA-1L Gen 2s. You could always Bi-wire, but here too a good 10 gauge wire from say BlueJeansCable and you wouldn't even have the need to Bi-wire.
OK, well that's my two cents from hands-on Listening in my own home (I own XPA-3 Gen 1, XPA-1L Gen 2, XPA-1 Gen 2, ADCOM GFA-5802, and Bryston 6B-SST).
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Post by garbulky on Jan 18, 2016 13:11:07 GMT -5
I too would reccomend XPA-1 gen 2s over XPA-1 L bi amping.
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Post by novisnick on Jan 18, 2016 13:59:06 GMT -5
I too would reccomend XPA-1 gen 2s over XPA-1 L bi amping. I'll make sure I call you for help when its time to move the XPA-1s,,,,,,,,,,   |
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Post by donmobliano on Jan 18, 2016 14:44:51 GMT -5
Good to know, thanks. I am concerned about wattage from the XPA-1 with the 75F's. The recommended amp wattage from paradigm is something like 200-500 if I recall. The XPA-1 into 4 ohm is 1000 watts.
I do have one XPA-1, so maybe I will bi-amp one speaker and run the other off the XPA-1 and see how the sound compares.
Thanks again for the feedback!
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